As well as the pea soupers, the Tower and Big Ben, cockneys and City gents in bowlers, there are some wonderful and unexpected pictures in a survey of 20th-century photography in the capital, writes Laura Cumming

The big art institutions here are finally catching up with their American counterparts, with a new photography gallery at the V&A, increased prominence at the Tate and exciting plans elsewhere. Sean O'Hagan asked four top curators about the state of the art